1. Field of the Invention
The present invention relates generally to a moving head for semiconductor wafer polishing apparatuses and, more particularly, to the polishing of a semiconductor wafer material from which an integrated circuit is made. That is, the present invention relates to a moving head for semiconductor wafer polishing apparatuses, which detects vibrations transmitted to a wafer and outputs signals indicating frictional force and pressing force acting on the wafer, using a load cell and a piezoelectric sensor installed in the moving head so as to maintain optimum frictional force and pressing force relative to the surface of a polishing pad, thus realizing precise final polishing.
2. Description of the Related Art
Generally, since a wafer polishing process is a process for realizing final flatness and surface roughness, prior to a device assembly process, the wafer polishing process is very important. Because it is so important, a lot of research on wafer polishing process has been conducted by research workers in research laboratories. However, due to the special characteristics of wafers, the results of most of the research are not clear.
The final polishing process is conducted through the following method. That is, a wafer carried by a carrier is rotated on a polishing pad, so that the surface of the wafer is mechanically flattened. Simultaneously, slurry, which undergoes a chemical reaction, is supplied to the upper surface of the polishing pad, so that the wafer is chemically flattened.
Meanwhile, in order to achieve a higher removal rate in the final polishing process, the surface roughness of the polishing pad must be always kept constant. However, as the final polishing process is continuously performed, the surface roughness is reduced, and thus a polishing function is gradually lost. In order to prevent the loss of the polishing function, a device called a pad conditioner is used.
The pad conditioner is a device for optimizing the condition of the pad so that wafer polishing is normally conducted on the polishing pad. The pad conditioner functions to flatten the polishing pad and to prevent particles generated by a slurry solution or a polishing process from being deposited on the pad, thus preventing the pad from losing its function. Further, the pad conditioner helps the pad maintain constant surface roughness, in addition to evenly distributing the slurry solution.
However, when the pad conditioning operation is conducted, the pad conditioner is repeatedly used without checking the condition of the polishing pad using a sensor. Thus, it is impossible to know the condition of the pad.
FIG. 1 is a view showing a conventional chemical-mechanical polishing (CMP) apparatus. Referring to the drawing, the CMP apparatus includes a moving head 104. A wafer 100 is attached to the lower surface of the moving head 104 which is connected to a shaft 102. The moving head 104 is rotatably mounted to the upper portion of a main body (not shown). The moving head 104 is in close contact with the polishing pad 108 of a table 106, and is rotated while applying a predetermined pressure.
The polishing pad 108 is connected to a rotating shaft such that the polishing pad 108 is rotated by a drive means provided on the lower portion of the main body. The polishing pad 108 is coupled to a polishing retainer ring 110 to which the wafer 100, mounted to the lower surface of a platen of the moving head 104, is mounted.
Such a CMP apparatus is disclosed in Korean Patent Appln. No. 1997-705718, which is titled “Method of Determining Frictional Coefficient of Polishing Pad”. The method is problematic in that dressing is required every time a polishing process is conducted without monitoring frictional force or pressing force, so that the efficiency of the process is low. In other words, the frictional force of the moving head in the CMP apparatus is detected at the exterior, and thus the detected result may be slightly inaccurate due to factors interfering with the detection.
Further, U.S. Pat. No. 5,916,009 has been proposed, and is titled “Apparatus for Applying and Urging Force to a Wafer”. According to the cited document, a carrier includes a holder and a pressure-bearing member. A wafer is mounted to the lower surface of the carrier. A load cell and a spring plate are provided between the holder and the pressure bearing member, and are rotated by a rotating shaft. However, the conventional wafer polishing apparatus is problematic in that it is impossible to monitor frictional force and pressing force, which are important factors affecting surface roughness in the final wafer polishing process, in real time, and thus the efficiency of polishing the wafer is poor.